Percutaneous transluminal coronary angioplasty (PTCA) is a less invasive surgical alternative for patients with vessel narrowing due to atherosclerosis and other diseases and conditions. In a conventional PTCA procedure, a dilatation catheter is inserted into the cardiovascular system, under local anesthesia, to a desired position within the culprit vessel. The catheter includes an inflatable balloon formed of a non-porous membrane at its distal end, and means for inflating the balloon. As is illustrated in FIG. 1A, balloon 10 is positioned so that it traverses or crosses stenotic lesion 12 within artery 14. As is illustrated in FIG. 1B, balloon 10 then is inflated with a radiopaque liquid at relatively low pressures. This liquid compresses balloon 10 against lesion 12, and expands artery 14 in a direction generally perpendicular to its wall, thereby dilating the lumen of the artery. Such compression may cause damage within the arterial wall, illustrated by the wavy lines in FIG. 1B. Following this procedure, balloon 10 is deflated and the catheter withdrawn.
Despite the general success of PTCA, the dilated lesion can undergo an aggressive neointimal healing response resulting in restenosis within the first year after dilation, as is illustrated in FIG. 1C. Such restenosis may be amplified by abrupt recoil of artery 14 resulting from lesion elasticity, vessel dissection, vasospasms, or the like, e.g., resulting from damage to the intima or media of the arterial wall. Alternately, or additionally, restenosis of the artery may occur. For example, an inflammatory response to PTCA, e.g., due to damage to the artery, may induce tissue proliferation 12′ around the site of the stenotic lesion. Thrombotic occlusions may also block the artery near the site of the stenotic lesion. As FIG. 1C illustrates, restenosis of the artery may arise from a thickening of the arterial wall and/or a narrowing of the lumen of the artery, and the subject may need additional treatment in order to restore patency.
Stenting is a commonplace technique used to try to prevent and/or treat restenosis, and frequently is employed as an adjunct to PTCA. During the stenting procedure, a metal mesh (stent) is deployed against the wall of the dilated artery and serves as a scaffold to hold open the artery. However, stents may occlude due to thrombosis, or the formation of a clot in the stent. Because the stent is a foreign object, the body's immune system also may respond with cell proliferation, resulting in restenosis. Such proliferation may be reduced by coating the stent with drugs such as paclitaxel, to reduce the growth of neointimal scar tissue, but such drugs also limit healing of the arterial wall and thus increase the chance of delayed clot formation.
It has been suggested that restenosis may be reduced by applying a drug directly to the lesion during the PTCA procedure. For example, U.S. Pat. No. 5,306,250 to March et al. discloses a porous membrane that is mechanically or hydraulically expanded into contact with a stenotic lesion. After the membrane is expanded, a liquid containing a drug such as heparin or colchicines is caused to flow through the pores in the membrane and into contact with the lesion. The expansion and drug-delivery mechanisms are independent of each other in order to avoid leakage of the drug through the pores until the membrane is fully expanded.
U.S. Pat. No. 5,458,568 to Racchini et al. discloses a selectively permeable balloon that both dilates a passageway and delivers a drug, such as a fixative. The permeability of the balloon is controlled by wetting the pores of the membrane using a pressure based on the surface tension of the liquid, the contact angle of the liquid on the membrane, and the pore diameter, and/or applying a current, and/or applying high frequency sound waves. The fixative quickly kills or otherwise renders the tissue inert, and hardens the vascular structure in a dilated condition. Racchini et al. discloses that such fixation prevents or reduces re-closure due to vasospasm, and also retards or stops the biological processes that lead to restenosis.
U.S. Pat. No. 5,354,279 to Hofling discloses a catheter that includes hollow needles that can be used to inject medicine within the wall of a blood vessel.
Although the delivery of a drug such as heparin to a stenotic lesion may be useful, blood flowing through the artery may quickly wash the drug away from the affected area, thus reducing the efficacy of the treatment. Such drugs also have little effect on vessel recoil and vasospasm. While Hofling discloses needles for injecting a drug directly into the wall of a blood vessel, the number of needles that can be used is limited, thus constraining the extent to which the medicine can be delivered. Additionally, the gauge of the needles used is relatively large, which increases the risk of dissection. While fixation of an artery such as disclosed in Racchini et al. may reduce the chances both of restenosis and recoil, the mechanism by which this fixation is accomplished—killing and hardening arterial tissue—impairs the artery's ability to heal itself and may potentially damage the surrounding healthy tissue.
In view of the foregoing, it would be useful to provide a balloon that dilates a blood vessel and that may be used to deliver a therapeutic agent to the dilate blood vessel without rupturing either the balloon or the blood vessel.
It would also be useful to provide a balloon that delivers a therapeutic agent at a sufficient pressure and velocity to penetrate to a controlled depth within, or even beyond, the wall of a dilated blood vessel, without rupturing either the balloon or the blood vessel.
It would also be useful to provide a therapeutic agent that, when delivered to a controlled depth within, or even beyond, the wall of a dilated blood vessel, inhibits recoil and restenosis of the blood vessel without killing a portion of the blood vessel.